The present invention generally relates to storing electric energy by means of electrochemical storage units, capacitors with and without electrochemical components and the like, which are capable of at least supplying and possibly storing electric energy. For simplicity in the following such energy storages are referred to as electric energy storages.
Electric energy storages in the form of accumulators, capacitors or a mixture of these two components are increasingly gaining in importance in industry and private homes, since for instance the growing local generation of electric energy, frequently performed irrespective of demand according to the environmental conditions such as sun, wind, and the like, requires electric energy to be stored in times, in which excess electric energy is available. In this respect currently existing power grids are increasingly facing the problem that load peaks in industry and private homes may no longer be covered due to an imbalance between peaks of generation of regenerated energy and the actual load peaks, unless providing appropriate storage devices are provided. Also electric energy storage systems represent essential components in mobile applications that allow a desired level of mobility for a large number of applications due to the increasing performance of the energy storage systems. Examples for mobile applications of energy storages include small appliances, such as phones, mobile computers in any variation and the like. A further example for the application of efficient electric energy storages is electro mobility, which is gaining in importance and whose further growing significantly depends on the characteristics of the electric energy storage, such as the available storage capacity, the amount of power output and usable lifetime of the electric energy storage.
Generally, a plurality of electro chemical systems is available that are used for the construction of an electric energy storage, the difference being in particular the type of electrolyte materials used, materials of electrodes and the like. Presently, well established electrochemical energy storages based on lead are increasingly replaced with energy storages, such as accumulators on the basis of lithium, nickel metal hydride and the like. Electrochemical energy storages on the basis of lead are still widely used in mobile applications, such as in the form of batteries for vehicles, drive batteries for forklift trucks and the like, and are particularly frequently used as stationary battery systems for supplying stand-alone devices or as emergency power plant. Irrespective of the configuration of such accumulator systems, which will be referred to hereinafter simply as battery systems, it is extremely important, depending on the type of electric energy storage, to monitor the current operating state of the electric energy storage and possibly manipulate the state in order to maintain a long lifetime at the required output and input of electric energy and electric power, respectively.
Typically, the battery systems are built up from individual cells or blocks, which have a rated voltage depending on the specific design in order to obtain a desired total voltage as connection voltage of the battery system. Frequently a plurality of cells of the same type is connected in parallel to obtain a desired current rating. By parallel connection of individual cells typically a common connection voltage is obtained for this block of parallel-connected cells, thereby typically not requiring an individual monitoring of the connection voltage of each individual cell. Since the connection voltage of an individual cell does typically not correspond to the desired rated voltage of the battery system a plurality of cells or blocks, which may possibly include several parallel-connected units, are connected in series, thereby obtaining the desired rated voltage. In a series connection of individual blocks the input current or output current flows through each cell or block so that the current load is identical for each cell or block, while the resulting connection voltage corresponds to the sum of voltages of the individual blocks, which is typically correlated with the state of charge.
Upon repeatedly charging and discharging a portion of the stored electric energy or the total energy an increasing discrepancy of the individual voltages may be observed due to variations of the individual blocks, thereby increasing the risk for obtaining a growing difference between individual voltages of cells or blocks, thereby resulting, upon performing further cycles, in increasing differences in the state of charge, which may finally lead to overcharging, deep discharging or even polarity reversal of individual blocks and cells.
Therefore great efforts are being made in order to monitor appropriate parameters for charging and/or discharging of a battery system so as to obtain information on the current state of the battery system. To this end, for instance, current and voltage of individual cells or blocks are monitored in order to estimate the state of charge of each individual block or each individual cell on the basis of the input and output energy and/or on the basis of the currently determined connection voltage. Since also environmental factors, such as temperature, humidity, and the like, significantly affect the operation of the battery system, frequently also these parameters are monitored and evaluated so as to possibly take appropriate countermeasures, thereby contributing to higher performance and/or increased lifetime of the battery system. To this end electronic systems, hereinafter referred to as battery management systems, are increasingly used, which at least monitor certain characteristics of the battery system and possibly control the operation of the battery system. As an example, in some battery systems, in which overcharging may be a potential danger, a corresponding regulation of the charge current is performed such that a hazardous state of the battery system may be prevented. In other cases active and/or passive heating and/or cooling systems are provided so as to maintain the operating temperature within a specified range. Typically, such battery management systems also monitor the voltage of individual cells or blocks and indicate a state, in which a too pronounced deviation between the individual connection voltages occurs. Furthermore, in many battery management systems appropriate means are provided so as to achieve a charge balance or at least an adaptation of the state of charge of individual cells or blocks. Although such battery management systems typically allow an extended lifetime of the corresponding battery systems they nevertheless increase overall complexity of an electric energy storage, however, without significantly contributing to enhanced flexibility with respect to applicability of the electric energy storage.
It is therefore an object of the present invention to provide means in the context of electric energy storages, which allow, by using electronic components, an increased level of flexibility in the adaptation of electric energy storages to the use profile of external electric components.